As the creator of the video I have to agree.
The gem prices are rather insane, especially with Halloween.

But the trick stays the same. I do believe I state within the video (If I do not then I should have) that the trick with the gems is for making it cheaper.

The logical assumption should be that if the gem prices get too high and getting the mystic forge stones is not worth it for profit that you would just use a 4th exotic. But because of the market right now it is more of a gamble.

Also, this video was made a while ago. It is indeed more of a gamble these days.